Control system



June 17, 1930.

A. PINTO 1,764,886 CONTROL SYSTEM Original Filed Oct. 6, 1925 2Sheets-Shee't l I IIIIIIIIIIIII 47 IME? lL j 56 I /53 Dld@ X154 E/52 zlIl Hl25 f I l Dl45 E /57 FIG] INvENToI? ATTORNEY June 17, 1930.

A. PINTO 1,764,886

CONTROL `SYSTEM Original Filed Oct. 6l 1925 2 Sheets-Sheet 2 L H20@[H207 VOLTAGE |NVENTOR 5y 'VIN/fo! ATTORNEY Patented June 17, 1936PATENT OFFICE ANTHONY PINTO, or NEW Yonign. Y., JERSEY cITY, NEW JERSEY,

ASSIGNOR TO OTIS ELEVATOR COMPANY, OF A CORPORATION OF NEW JERSEY ICONTROL sYs'rnm original implication alaoetoher' 6,1925, serial no.

60,769.V Divided and this application ld April 27,

192s. serial No. 27s ,2so.

The invention relates to control systemsI and-particularly to controlsystems for elevators. 1 This application is a division of applica- 5tion Serial No. 60,769, tiled October 6, 1925.-

In elevator control systems where the elevator' motor' issuppliedwithfcurrent by a variable voltage generator, the generator isrequired to operateA over a wide range of E. M. F. values varying from amaximum in one direction t a maximum in the other. Where self-levellingapparatus is employed,

.y the generator is values of E; M. F. in bringing the car t0 a levelwith a desired landing. Due to the hysteresis of the iron of thegenerator field, the E. M. F. values obtained for a given value of fieldcurrent during levelling operation vary considerably, depending on theprevious 'magnetic state` of the machine and Whether the car .isapproaching the landing or returning to the landing after an overrun.Such variations in E. M. F.`values cause undesirable variations in theoperation of the car during the levelling period.

One feature of the invention resides in energizing the field Windingof agenerator in suchmanner that-the effects of hysteresis are obviatedduring periods when a low voltf 3g age'is desired.

Other features and advantages will become ap arent from the followingdescription, ta en in connection withthe accompanying drawings whereinone embodiment of the invention is illustrated and in which:

Uv various switches are separated in s uch nianrequlred tooperate at lowFigure 1 1s a diagram of a elevator control.

22. A resistance ner as `to render the circuits involved relativelysimple. Also the parts of other switches and apparatus are separated inthe interest of simplifying the diagram. For a clearer understanding ofthe invention, the stationary contacts of the switches are illustratedin cross section. It is to be understood that the system in whichillustrated lis chosen merel for convenience of description and that, athough described' in conjunction Witha car switch controlled system, theinvention isequally applicable to other types of elevator systems suchas push button control systems and to other systems motor supplied 'withcur-- employing a work rent from the generator of a motor generator set.Y

The motorV generator set comprises a driving motor 11, illustrated forconvenience of l description as of the direct current type, and

a Ivariable voltage direct current generator 12. The armature of thedrivmg motor is designated 13 and its field winding 14.- The theinvention is armature' of the generator is designated 15 and its serieseld winding 16, its .separately excited eld winding being arranged intwo portions 17 and 1 8. The elevator motoris designated as a whole bythe numeral 20, 1ts armature beino' designated 21 and 1ts field winding22. adjustable resistance 23 is arranged in shunt to the generatorseries field winding. Discharge resistances -24 and 25 'are provided forthe portions 17 and 18 respectively ofthe generator separately excitedfield winding. Discharge resistance 26 1s provided for the elevatormotor field winding 27 is provided f or controlling the strength-0f thegenerator iield an therefore the voltage applied to the elevator motorarmature during car switch operation.

Another resistance 28 is provided for controlling the strength of thegenerator separately excited field during levelling operation.

resistance 29 controls the strength of the vator motor field duringdifferent conditions of operation. 30 is the release coil for th vatormotor electromagnetic brake: Thls coil is provided with dischargeresistances 31, 32 and 33 for contro g the a ppl1cat1on of the brakeunder different condltions of operation. 34 and 35 are the up slow speedcontacts and the down slow speed contacts re.

spectively of the levelling switch, the levelling switch up Aand downfast speed contacts being designated 36 and 37 respectively. 38 is thearmature and 40 is the field winding of the motor 41 lfor moving therollers of the levelling switch into position to clear the levellingcams. 42 is the armature and 43 is the field winding of the door controlmotor 44. 45 and 46 are the direct current supply mains. 47 is a doublepole lmife switch for connecting the system to the supply mains. Inorder .tol suit the type of diagram employed, the blades of this switchare shown separated.

'The car switch is designated as a whole by the numeral 48. 50 is thesafety switch in the car. The series of door contacts are indicated by asingle set of contacts 51. The gate .contacts are indicated as 52. Thevarious safety, limit, stop and emergency switches are omitted in orderto simpli The electromagnetic. swltches have been designated as follows:

v Afpotentialswitch,

B-up main direction switch,

own main direction switch, D-first accelerating switch, E-secondacceleratlng switch, F-series field switch, G-series field relay, H-mainbrake land field switch, J-door control motor switch, K-door controlmotor maintaining relay, L-field control switch, M--maintaininfr relay,N-sequence re ay, O-accelerating relay,

P-hard brake switch, R-levelling control relay, LB-up levellingdirectionswitch, LC-down levelling direction switch, LH-levelling brake and fieldswitch, LF-fast speed levelling relay. y Throughout the descriptionwhich follows, these letters, in addition to the usual referencenumerals, will be applied to the parts of the above enumerated switches.For example, contacts B 111 are contacts on the u main direction switch,whil'e actuating coll A 53 is the coil that operates the potentialswitch. The electromagnetic switches are' shown in their deenergizedpositions. Reactances are similarly designated by the char- 'F acter X..

Upon the closing of the knife switch 47, the driving motor 11, elevatormotor field winding 22 and potential switch actua ti coil A 53 areenergized, the circuit for coll A53 being through safety switch 50. Thedriving motor starts in operation, bringing the generator 12 up to fullspeed. The series field windingv and startin driving@ motor are omitteto simplify the description. With the elevator motor at the description.

rest, the current supplied to its field winding 22 is reduced by section54 of resistance 29, providing what may be termed a standing field. Thecircuit for the elevator motor field winding may be traced from thelefthand blade of switch 47, line 55, -by way of line 56 through fieldwinding 22, resistance section 54 and second accelerating switch .causeof the time constant involved in building up. The potential switch, uponoperation, causes the engagement of contacts A 60 and A 61, preparingthe circuit for the generator .separately excited field winding, theelectromagnetic brake release coil and the control` circuits. cuits sofar described might be termed norma Referring briefly to Figure 2, thecar switch 48 comprises a set of u contacts 62, 63, 64, and 66 and a setof own'contacts 67, 68, 69, and 71. A conta-ct segment 72 for bridgingthe contacts of each set is mounted on the segmental support 73 ofinsulating material.: A cam 74 is formed on the support above the pivotpoint75. The cam isformed with a centrally disposed de- 7 of the gateand door switch 78 extends with the car switch in neutral or offposition. The switch 78 is pivoted at 80 so that movement of the carswitch in either direction causes the engagement of the switch contacts.The car switch is operated by means of a control handle 81. It ispreferred to The condition of the cirprovide centering'springs (notshown) on the car switch to cause it to be returned to off position whenreleased by the operator.

Referring back to Figure 1, assume that the system is designed for aninstallation of several floors and that the car is at rest at the firstfloor with the gate and door open. In the start-ing operation, the'operator rst gives the car switch a slight initial movement to effectthe closure of the gate and door switch 78. For convenience ofdescription,

this switch is arranged to complete a circuit' for the door controlmotor switch actuating .coil J 82. This circuit may be traced from theleft-hand blade'of switch 47, by way of line 55 through contacts A 60,by way of line 83 through coil J 82, resistance 84 and switch 78, line85, switch 50, line 86, line 58, to the right-hand blade of switch 47The door control motor switch, upon operation, causes means forwthcrMtheengagement of contacts J 8'7, completing the circuit for the doorcontrol motor 44. This circuit may be traced from the left- ,handbladeof switch 47 by way of line -55 through contacts A 60, by way ofline 88 y through contacts J v87, door control motor vway door 109.

vto open them,

' operates upon the field winding 43'and armature 42, by way of line 58through contacts A 61, to the righthand blade of switch 47. a

Referringagain to Figure 2, motor 44 operates pneumatic gate' and dooroperating mechanism, as for example through linkage 90 to'move valve 91for gate engine 92 to gate closed position and to withdraw theretiringcam 93 from engagement with the roller provided on the end ofthe door engine valve lever 94. The lever 94 is operated by aspring tomove valve 95 for the door engine 96 to -door closed position. The gateand door engines operate through mechanism not shown to close the'cargate 99 Yand hatch- V`It :is'to be understood that a door Vis providedin the hatchway at each landing.

Referring back to Figure 1, if the operator, after `he has closed thegate and door, desires movement, he may do so by releasing the carswitch to return to 0H position. This causes the opening of the gate anddoor switch 78 with the consequent deenergization of coil 82and theseparation of contacts J 87. In this manner, the circuit *for the motor44 is broken. The spring 97, shown in Figure 2, deenergization of motor44 to move valve 91, and, through cam 93 and lever 94, valve 95 intopositions to cause the reverse operations of the engines 92 and 96 toopen the gate and door. Obviously other forms of power operated gate anddoor mechanisms, such as electric in may be employed without departing:trom the spirit of the present invention.

Assuming that the gate and doors are closed, the gate contacts 52 anddoor contacts 51 are in engagement. The operator may now move the carswitch to full operated position tostart the car in the up direction. Itis to be noted that the gate and door switch 78 remains in closedposition so long as the car switch is' moved out offne'utral position.Upon the engagement of contact segment 72 and contact 64, circuits aresimultaneously completed Jfor the oppositely wound coils 98 and N 100 ofthe sequence relay, actuating coils R 240 of the levelling controlrelay, H 101 of the main brake and field switch and 102 of the up maindirection switch being 1n the circuit for coil N 100. The engagement ofthe contact segment and contacts 65 and 66 prepares circuits for theactuating coils of: thel accelerating switches.

The circuit for coil N 98 of the sequence relay nay be traced rom theright-hand blade of switch 47, by way'of line 55 through contacts A 60,by way of line Y108 through'coil N 98 and resistance 104, contacts 62and 64 of the cal' switch, by way o line 105'through conor if he desiresto arrest their` lieu of pneumatic,

"bil B 102, contacts B110 separate and may be traced from the right-handblade of switch 47, by wa of line 55 through contacts A 60, by way oline 107 through door contacts 51, gate contacts 52, sequence relacontacts N 108, and coils R 240, N 100, 101 and B 102, contacts 63 and64 of the car Switch, to the right-hand blade of switch 47 as abovetraced. The purpose of the sequence relay N is to insure the closure ofthe gate Iand doors before starting the car. Coils N 98 and N 100, beingdifferentially wound, oppose each other, when energized simultaneouslyto prevent the operation of the relay. If either coil is energized aheadot the other, or if either coil alone is energized, contacts N 108separate, preventing the starting of the car. if either the gatecontacts 52 or any of the door contacts 51 are separated at the timethat cars switch segment 72 engages contacts 64, coil J eration of theup main direction switch to effect the starting of the car. The gate anddoor switch 78, therefore, is closed by the initial movement of the carswitch so that the gate and door contacts may be closed before theengagement of segment 72 and contact 64. However, if the car switch ismoved into position where segment 72 engages contact 64 before theclosure of the door and gate contacts, the sequence relay operates toprevent the starting of the car.' Thus it is impossible to start the caron the door or gate contacts.

Assuming that the sequence relay has operated, in order to start thecar' the car switch is returned to a position with segment 72 disengagedfrom contact 64, deenergizing coil N 98 to permit contacts N 108 toreengage. the gate and door` are closed, the car switch may be returnedimmediately to full on position. Otherwise, closing of the gate and doormust be effected before the car switch is moved into full on position.

The levelling control relay R, upon opera- N tion, causes the separationof contacts R 241 operation of the up main direction switch in responsetothe energization of its actuating conand B 113 engage. The

tacts B 111, B 112 B 110 breaks the cirseparation of contacts cuitleading from the car switch down feed -up main direction switch holdingcoil B 115 and the main brake and field switch holding coil H 116. Theengagement of contacts B 111 and B 112 completes a circuit for thegenerator separately excited field winding.

This circuit may be traced from the left-handy blade of switch v47, byway of line 55 through contacts A 60, resistance 27 and contacts B 111,by vway of line 117 through field' control switch contacts L 118,through portion 18 of the separately excited field winding, by way ofline 120 through contacts L- 121 and portion 17 of the separatelyexcited field winding, by way of line 58 through contactsl B 112 andcontacts A 61, to the right-hand blade of switch 47. y

The main bra-ke and field switch H operl at-es simultaneously with themain direction switch B. Switch H, upon operation, causes the separationof contacts H 119, H 122 and H 123 and the engagement. of contacts H124, H 125, H126 and H 127. The separation of contacts H 119 disconnectsthe generator separately excited field winding from the generatorarmature. The purpose of this arrangement will be explained later.Contacts H 122 are in thecircuit for the field control switch actuatingcoil L 128. The purpose of this arrangement also will be explainedlater. The separation of contacts H 123 disconnects resistance 33 fromacross the brake release coil 30. Resistance 33 being of low ohmicvalue, its disconnection before contacts H 124 engage prevents excesspower consumption from mains 45 and 46. The engagement of contacts H 127establishes a c1rcuit for the door control motor maintaimng relayactuating coil K 130. This circuit may be traced 'from the left-handblade of switch 47 by wa of line 55 through contacts A 60, by way o line83 through coil J 82, by way of line 131 through up levelling directionswitch conta cts LB 132, down levelling direction switch contacts LC133, contacts H 127 and coil K 130, line 85, to the righthand blade ofswitch 47 as previously traced. The engagement of contacts H 125 furtherprepares the circuits for the actuating coils of the acceleratingswitches.' The enga ent of contacts H 126 short-circuits sectlon 54 ofthe elevator motor field resistance 29,-permitting the motor field tobuild up to its full strength. The engagement of contacts H 124 compcoil 30. This circuit maybe traced from the left-hand blade of switch 47by wa of line 55 through contacts A 60, by -way o line 134 throughcontacts 135 operated by the brake,

:brake release 'coil 30 and contacts H 124, bv

switch7 in etes the 'circult for the brake release wa of line 58 throughcontacts A 61, to the rig t-hand blade of switch 47.

.The door control motor maintaining' relay coil K 130 in the circuitabove traced is subject to the potential drop acro resistance 84. Thesystem is arranged so that the. voltage thus applied to coil K 130 issuflcient to effect `the operation ofthe relay. Contacts K 136 engage,upon the o ration of the relay, to by-pass contacts 127. The purpose ofthis arrangement ,will be seen from later description.

The brake release coil 30 vbeing energized, the elevator motor fieldbeing connected directly to the( mains 45 and 46 and current beingsupplied from the generator armature 15 to the elevator motor armature21, due to the energization of the portions 17 and 18 of thev generatorseparately excited field winding, the elevator motor starts. The portion18 of the generator separately excited field winding as now ,connectedthe portion 17.

As the brake releases, the brake switch contacts 135 separate to insertcooling resistance 137 in series with the brake release coil. Thesebrake switch contacts are preferably arranged to be separated at the endof the releasing operation. Separation of contacts 135 also breaks theshort circuit around coil O 138, permitting the operation o'f theaccelerating relay O. This relay operates to cause the engagement ofcontacts O 140, completing the'circuit for the first acceleratin iswitchl actuating coil D 141. The purpose o this arrangement is toutilize the time constant of the brake for .timin the acceleration ofthe motor, more s ecifica y, for timing the operation of the rstaccelerating switch. Although thev brake at the same time that power issupplied to the motor, the brake shoes do not hft at once because of theinherent time constant of the brake magnet and because the brake shoesand lever arms represent considerable mass to be set in motion. Thecircuit for coil D 141 completed by contacts O 140v may be traced fromthe right-hand blade of switch 47, by wa of line through contacts A' 60,by way o line 107 through the door contacts 51, gate contacts 52' andcontacts N 108, by way of line 142 through'contacts H 125, contacts O140 and coil D 141, contacts 65 and'64 of the car switch, to theright-hand blade of switch 47 as previously traced.

The operation of the first accelerating ll'ponse to the energization ofits actuatmg ooi causes the en ent of oontats D 143, D 144, D 145 an D146. .The eng t of contacts D 143 completes the circuit for the levellnswitch motor 41. This circuit may be trace blade yof switch 47 by way ofline 55 through release coil is energized from the left-hand contacts A60, by way of line 147 through 38 ofmotor 41, by way of line 58 throughconspeed of the elevator motor increases. The tacts A 61, to theright-hand' blade of switch separation of contacts E 57 removes theshort Thev starting of the car in the down direccircuit Yfor section 167of resistance 29 in thea energization, to move the levelling switchopelevator motor field winding circuit, bringing, s-eratingrollers so asto clear the `levelling the elevator motor up to full speed. 7o camsduring movementof the car. This op- The starting of the car in the downdireceration will be explained later. The engagetion is accomplished ina similar manner and ment of contacts D 144 completes the circuit willbe only brieiy described. The operator for holding coils B 115v and H116. This irst moves the car switch into position to lo circuit may betraced from the left-hand cause the closure of the gate and door and 75blade of switch 47, by Way 'of line 55 through/then into full onposition where its contact contacts A 60, by way of line 148 throughcoil segment 72 bridges contacts 67, 68, 69, 70 and H 116. and contactsD 144, by way of line 150 71. Thus the -circuit is completed for thethrough coil B 115 and contacts B 113, line dwn main direction switchactuating C011 151, line 85, to the right-hand blade of switch C 168.This circuit may be traced from the 8o f 47 as previously traced, Thepurpose of the left-hand blade 0f SWCh 47, hIOUgh 0011 H energizationofthese holding coils will be 101 aS PIeVOllSly traced, by Way 0f line170 seen from later description, The engage.. tlirugh Coil C 168, Cal'Switch contacts 68 ment of contacts D 146 completes the circuit and 69,by Way 0f 11116 171 thrOugh Contacts .20 for the second acceleratingswitch actuating B 110, 11116 85, t0 the right-hand blade O- 85 K coil E152. This circuit may be traced from switch 4:7 as previously' traced.The circuit the left-hand blade of Switch 47, by way of for C011 'N 981S by ,Way of 1111e 1,72 The C11'- line 55 through contacts A 60, by wayof line 6F11? 01 C011 141 1S by Way 0f Ime 17,3' The 107 through doorcontacts 51, gate contacts ell'eult for C011 11.15215 by Way 0f -1me174- 52 and contacts N 108, by way of line 142 .The dOWIl mln'dlleetlOPSWltehauPoD opera' 90 through Contacts H 125, by Way of line 153 tion,causes the separation of contacts C 106I through contacts D146,reactance X 154 and and the engagement et Contacts C 17,5, C 17d coil E152, car switch contacts 66 and 64, to and C ,177 these eentaetseerrespeltdmg Wlth the righ/band blade of switch 47 as previ,.- up maindirection switch-contacts B 110, B

ously traced.` The engagement of contacts 111,13 112 andB113TeSPeCt1Ve1y- 'The held 95 D 145 short-circuits section 155 ofresistance mg e011 0f the down direction Switeh 1S des' 27, increasingthe voltage applied to portions ignated C 17,8- Ful'thef than this, theePePe" 17 and 18 ofythe generator eld winding. tlon et Stdrtm'g the C31'111 the down dl'eetlen Thus the generator E. M. F. is increased, in- 1S.the Same as described fel' Startmg 1t in the f5 creasing the speed'o'fthe motor. up dl'eetlen- Y g The second accelerating switch E does notAsellme that the Car 1S Tunning m the 1P operate immediately the circuitfor its actudlreetlfm and that the Operator. eelltefs the v ating Coilis. Completed, its action being Q car switch between the second andthird iioors layed by the effect of reactance X154- Upg in order to stopat the thirdV iioor landing.

kc on operation', contacts E 156 and E 57 sepa- Thus the Contact Segment72 moves ott con' 105 rate and contacts E 157 and E 158 engage. tacts 6665 64 and. 63 and the @mints tqr The separation of contacts. E 156removes the Second acceterattng Switch actuattng cotl the shunt circuitaround a portion of resist- E 152 ttst accetetatmg Swltch .actuatmg(5011' ance 166. The separation of contacts E 156 D 141, 1113111blfikqalld field switch actuating before contacts E 158 engage preventsexcess 30.11 11.101 up mam dtrectlon Swttthttctuat' 110power'consumption from mains 45 and 46. mg C011 B 102.. level-1mgcotltrol relay C011 The engagement of contacts E 158 complete's R 240sind Sequence relay 0,0113 N 98 and'N the circuit for the firstaccelerating switch 100 are broken' The 1eV.e11mg .conttot relay holdingcon D ici and the maintaining may and the Seme lertmgswltch drop011tactuatin coil M 162. This circuit ma be traced` fftom the left-handblade of svgitch mam brak? and eld .Swltch and up mam d1' 47 by Way ofline 55 through Contacts A 60, rection switch are maintainedoperated,4how by way of line 151 through contacts E 158, ever by httdmgc0115 D HMH .116 al1-1.13 reactance X 163, CoipD 161 and coil M 162, 115respectively, The deenergization of coils une 85, to the right-hand10i-ade 0f Switch 4.7 N 9eme N 100 1S 111 Preparan@ for #heeel-It 120 aspreviously traced. The maintaining relay Sta 1'tm-f ,01}emt10n ,1t 1S tobe doted that contactsM 164 are thus caused to by-pass SWlteh .18 1SOpened by the eente'mg 01 the Contacts D 144, The purpose of this arcarswitch.l The circuit for coil J 82,'ho`wrangment will be describedltelg` The enever, is maintained through contacts 127 immediately. Thefirst accelerating switch,

C9 gageinent of contacts E 157 short-circuits and K 136 in parallel and.C011 K 130- 125 sections 165 and 166 of resistance 27 to in- Thelevelling control relay, upon dropping crease the voltage applied toportions 17 and out, causes the reengagement of contacts R 18 of thegenerator Bseparably excited field 241. As previously stated, thelpurpose of this winding. The E. M. F. of the generator, relay will beexplained later. e

't5 therefore, increases to its Jfull value and the The secndaccelerating switch, upon drop- 130 ping out, causes the separation ofcontacts E 157 and E 158 and the reengagement of contacts E 57 and E156. The separation of contacts E 157 reinserts sections 165 and 166 of-ts@resistance 27 in series with the generator separatel excited fieldwinding to decrease the E. F. of the generator. The engagement ofcontacts E 57 4short-circuits section ered and the strength of theelevator motor field increased, the s ed of the elevator motor isdecreased. 'llaie separation of contacts E 158 breaks the circuit forholding coil D 161 and coil M 162. The first accelerating switch -D andmaintaining relay M 4do not drop out immediately, however, their actionbeing delayed by the effect of reactance X 163 in series with the coilsand the discharge resistance 160 in arallel with the reactance and thecoils. T e engagement of contacts E 156to short-circuit a portion ofresistance 160 is el'ectiveto rolong the time element of the switch andre a The time element'may be adjusted to the esired value by changingthe'amount of the-resistance portion shortcircuited. Relay M ispreferably adjusted to hold in at a smaller current value than theaccelerating switch D. This may be readily accomplished due to the factthat the relay is much smaller and therefore lighter in constructionthan the accelerating switch and requires less current to hold in.

The first accelerating switch, upon dropping out, causes the se arationof contacts D 143, D 144, D an D 146. The separation of contactsD 144 isin preparation for the next starting operation, contacts M 164 remaininin engagement to maintain holding coils 116 and B 115 energized. Theseparation of contacts D 146 also is in pre aration -for the nextstarting o eration, t e circuit for coil E 152 having en broken by themovement of the car switch as above described. The separation ofcontacts D 145 removes the short circuit for section of resistance 27,.decreasin the strength of the generator field. Thus te generator E. M.F. is again decreased and the speed of the elevator motor is reduced. Itis to be understood that resistance 27 may be controlled in any numberof steps, two being shown merely for convenience of description.

The separation of contacts D 143 deenergizes the levelling switch motor41. In this manner the operating rollers of the levelling switchareextended for engagement by the levelling cams. Referring briefly toFigure 2, the levelling switch motor is operatively connected to thelevelling switch by means of an arm on the motor shaft, a connectinglink 181 and a lever 182. In the starting operation, the motor 41 beinenergized, arm 180 rotates, acting through link 181 and lever 182 lingcams and 186 during motion of thel car, a stop being provided todetermine the extent of the movement. It is to be understoodI thatlevelling cams are provided for each oor. The levelling switch ispivoted on a bracket 187 secured to the car frame. In the stoppingoperation, upon the deenei'gization of the levelling switch motor, aspring (not shown) moves the lever 182 and therefore the levellingswitch .back into the first described position with the rollers 183 and184 extended for engagement by the levelling cams. Each pair oflevelling switch contacts 34, 35, 36 and 37 comprises a stationarycontact and a movable contact operated by the engagement of itscorresponding roller and levelling cam. The fast speed contacts 36 and37 are' arranged to separate before their corresponding slow speedcontacts 34 and 35 in the levelling operation. Springs (not shown) are"provided for causing the separation of the contacts of the airs as thelevelling operation is effected and) stops are provided for determiningthe extent of movement of the rollers as they ride ofi' the levellingcams.

It will be assumed that the car has not reached the landing and that theup levelling switch operating roller 183 moves onto the vertical surfaceof up levelling cam 185 before relay M drops out. The engagement oflevelling switch up slow speed contacts 34 completes a circuit fortlie ulevelling direc- B 188 and the tion switch actuating coil levellingbrake and field switch actuating coil LH 190. This circuit may be tracedfrom the left-hand blade of switch 47, by way of line 55 throughcontacts A 60, line 191, levelling switch contacts 34, b way of line 192through coil LB 188 and coil 190, by way of line 85 through levellincontrol relay contacts 241, to the right-hang blade of switch 47 aspreviously traced. The enga ement ofthe levelling switch up fast spcontacts 36 coinpletes the circuit for fast speed levelling relayactuating coil LF 193.- This circuit may be traced from the left-handblade of switch 47 by way of line 55 through contactsA 60, line 191,levelling switch contacts 34, line 194, levelling switch contacts 36, byway of lline 85 through coil LF 193 and contacts R 241,

to the right-hand blade of switch 47 as previously traced. It is to benoted that, due to the fact that the circuit for coil LF 193 is `throughlevelling switch slow speed contacts 34, the circuit for coils LB 188and LH 190 must be made in order that the circuit for coil LF 193 may becompleted.

The up levellingldirection switch LB, upon operation, causes theseparation of contacts vLB 132 and the engagement of contacts LB 195, LB196 and LB 197. Contacts LB 132 lim ` relay actuating coil (ir-198 andup hard brake be traced from the coil K 130 and switch switch actuatlngcoil P 200. This circuit ma left-hand blade of switc 1 47, by way ofline 55 through contacts A 60, by way Vof line 201 through contacts LB197,

coil G 198, coil P 200, and portion 202 of re-" actance X 203, line 204,by way of line 58 through contacts A 61, to the right-hand blade ofswitch 47.

The levelling brake and field switch, operating simultaneously with theup levelling direction switch, causes the separation of contacts LH-205,LH 206 and LH 212 and the engagement of contacts LH 207, LH '208, LH 210and LH 211. Contacts LH 205 are in the circuit for resistance 33 acrossthe brake release coil. Contacts LH contacts lH 119 in the circuit forconnecting the generator separately excited field winding to thegenerator armature. Contacts LH 21,2 break the shunt circuit, comprisingresistance 160, for coils D 161 and M 162. Contacts LH 207 by-passcontacts H 124 in the circuit Jfor the brake release coil. Contacts LH208 bypass contacts H 126 in the circuit for section 54 of the motor eldresistance 29. Contacts LH 210 are'in the circuit for the tield control-switch actuating coil L 128. The engagement of contacts LH 210 iswithout effect at this time'as contacts H 122 are separated. The purposeof contacts LH 205, LH 206, LH 207, LH 208 and LH 210 will be seen asthe description proceeds. Contacts LH 211upon their engagement, preparea circuit for shortcircuiting section`155 and adjustable section 165 of,resistance 27 f or the generator separately excited field winding.

Thefast speed levelling r lay, upon operation, causes the engagement ofcontacts LFV 213 and LF 214. The engagement of contacts LF 213 preparesa circuitfor short-circuiting the adjustable section 166 of resistance27 for the generator separately excitedtield winding. The enga ement ofcontacts LF 214 by-passes contacts B 132, LC 133, H 127 and K 136, 78through resistance 84 in a circuit for coil J 82 of the door controlmotor switch. Since the engagement of contacts LF 214 generally occurssubstantially simultaneously with the separation of contacts LB 132, theswitch J does not drop out. Even if switch J should drop out, theimmediate reenergization of coil J 82 upon the engagement of contacts LF214 would prevent the operation of the gate and door operating 206 arein series with effect, the circuit for the brake coil K 130, however, isbroken by the separation of contacts LB 132.

The `separation of contacts LH 212 to break the circuit for resistance'160 as. above set forth causes relay M to dropout and separate contactsM 164. As a result the circuit for holding coils 115 and H 116 isbroken, permitting the up main direction switch and main brake and fieldswitch to drop out. Switch B, upon dropping out, causes the separationof contacts B 111, B 112 and B 113 and the engagement of contacts B 110.The separation of contacts B 113 and the engagement of contacts B 110 isin preparation for the next starting operation. The separation ofcontacts B 111 and B 112 is Without etect as they are by-passed bycontactsLB 195 and LB 196 to maintain the energization for the generatorseparately excited field winding. The switch H, upon dropping out,causes the separation -of contacts H 124, H 125, H 126 and 127 and theengagement of contacts H 119, H 122 and H 123. The separation ofcontacts H 125 and H 127 is in preparation for the next startingoperation. The separation of contacts H124 and H 126 is Without releasecoil 30 being maintained by contacts LH 207 and section 54 of resistance29 remaining shortcircuited by contacts LH 208. ,The engagement ofcontacts H 119 and H 123 also is without effect as the circuitsforreconnecting the generator separately excited ield Winding to thegenerator armature is maintained broken by contacts LH 206 and the shuntcircuit for the brake release coil 30 comprising resistance 33 ismaintained broken by contacts LH 205. The engagement of contacts H 122,however, completes the circuit for the field control switch actuatingcoil L- 128. rQihis circuit may be traced from the left-,hand blade ofswitch 47, by way of line 55 through contacts A 60, by way of line 215through contacts H 122, contacts LH 210 and coil L 128,

line 85, to the right-hand blade of switch 47 force which opposes themagnetizing forcedue to-portion 17.

Discharge resistances 24 and 25 act to smooth out not only the changesin generator E. M. F..due to the reinsertion of resistance 27 in circuitwith the separately excited ield winding in steps, but also the changedue to relay contacts LF 213. With contacts L 118 and L 121 separatedand contacts L 216, L 217, L 218, L 220 and LF 213 in engagement, an E.M. F. is generated which causes the ele- 15. vator motor to run at asuitable fast levelling speed, as will be seen from later description.

Relay G and switch 1:v do not operate im-.

mediately their actuating coilsare energized, their action being.delayed by reactance X zo 203. Switch P, however, is adjusted toAoperate almost immediately and, upon operation,causes the separation ofcontacts P 221, disconnecting resistance 32 from across the brakerelease coil 30. Relay G, upon operation, causes the engagement ofcontacts G 222, completing the circuit'- for the series field switchactuating coil F 223. This circuit may be traced from the left-handblade of switch 47, by Way of line 55 through contacts A 60, by Way ofline 224 through contacts G 222 and coil F 223, by way of line 58through contacts A 61, to the right-hand blade of switch 47. Switch F,upon operation, causes the separation of contacts F 225,

35 breaking the circuit including resistance 23 in shunt to thegenerator series fieldl winding 16. The generator series field is fsowound that, without the parallel resistance 23, it would have too greatan effect for proper operation of the car. The desired compounding isobtained by employing the low resistance shunt. lUpon separation ofcontacts F `225, the strength` of the series field is in creased `forthe levelling operation so as to aid in' bringing the motor to a stop.The short delay yin the action of relay G, and therefore `switch F, uponthe initiation of the levelling operation, is desirable in order thatthe current in the` generator armatureelevator motor armature circuitmay ad'ust itself t such avalue that proper series eld strength duringthe levelling operation may be obtained.

As the car 'nears the third floor landing, roller 183 rides ofi' theverticalsurface onto .v the oblique surface of cam 185. This results inthe separation of levelling switch up .fast speed"contacts 36,deenergizing fast speed levelling relay coil LF'193, Relay LF, upon droping out, causes the separation of 'contacts F213 and LF 214. The-sep'aration of contacts LF 213 removesf'the short circuit aroundsection 166of resistance 27, sections 155 and 165 remainingshort-circuited by contacts LH 211. The generator E. M. F.

is thus lowered and the elevator motor runs at its slow levellin speed.The separation of contacts LF 214 reaks the circuit for the door controlmotor switch coil J 82. Switch J. upon'dropping out, causes theseparation of. contacts J 87 to deenergize the motor 44, thus effectingthe automatic gate and door opening operation. The gate and dooroperating mechanism functions in the saine manner as described foropenin the gate and door in response to centerin t e car switch. In thismanner the automatic gate and door opening operation is timed so thatthe gate and door open as the car stops at the landing. It is 'to benoted, however, that the automatic gate and 'door opening operationcannot take place until the levelling switch fast speed contactsseparate. f

Shortly before the car reaches the exact level with the landing, theroller 183 rides off the oblique surface of cam 185, thereby separatingthe levelling switch up slow contacts 34. The circuit for coils LB 188and LH 190 is thus broken. Switch LH drg out, causing the lseparation ofcontacts 207, LH 208, LH 210 and LH 211 and the reeno'agement ofcontacts LH 205, LH 206 and rLH 212. The enga ment of contacts LH 212 isinipreparation' or the next start' operation. The separation of contactsL 211 also is in preparation for the next starting operation, thecircuit for the generator separately excited field winding being brokenas a result of the separation of up levelling direction switch .contactsLB 195 and LB 196 as will be set forth below. The separation of contactsLH 207 breaks the circuit for the brake release coil 30 and theaccelerating relay coil O 138. Due to the fact that the coil 30discharges into resistance-31 of relatively high ohmic value, a hard aplication of the brake is obtained. The. acce eratving relay O drops outseparating contacts O 140 in preparation or the next startin operation.The separation of contacts LH 208 reinserts section 54 of resistance 29in seriesC with the elevator motor field winding, reducing the currenttherein to a standing field value. The separation of contacts LH 210'breaks the circuit for the field control switch coil L 128, the switchdropping out in preparation for the next starting operation. It is to benoted that the separation of contacts L 216 and L 217 and the engagementof contacts L 118 and L 121 reconnects the portions 17 and 18 of theseparately excited I field winding for cumulative action. Thereengagement of contacts LH 206 reconnects the generator separatelyexcited field winding to the generator armature. The polarity of thisconnection is such that the generator sends current through the fieldwinding in such manner as to op se the flux which roduces the generatorM. F., thus tending to destroy the residual flux of the generator ifield.

Up levelling direction switch LB, dropping out along with switch LH,causes the separation of contacts LB 195, LB 196 and LB 197 and theengagement of contacts LB 132. The engagement of contacts LB 132 is inpreparation for the nexts'tarting operation. The separation of contactsLB 195 and LB 196 disconnects the generator separately excited ieldwinding from the mains as indicated above. The separation of contacts LB197 breaks the circuit for coils G 198 and P 200. The relay G drops outimmediately, but the dropping out of switch P is delayed slightly due tothe eil'ect of the reactance X 203 and discharge resistance 226. It isto be notedv that the discharge current. for up coil P- 200 and thereactance passes through down coil P, 227 in such direction as to causecoil P 227 to assist coil P 200 in maintaining switch P in operatedcondition. Relay G, upon dropping out, causes the separation of contactsG 222 to deenergir/:ev coil F 223, switch F dropping out in turn tocause the engagement of contacts F 225. The engagement of contacts F 225reconnects resistance 23 in parallel with the generator series fieldwinding 16. Switch P, upon dropping out, causes the engagement ofcontacts-P 221.

Thus the brake being applied and the gen- .erator separately excitediield winding being disconnected` from the mains, the car is brought torest level with the third iioor landing. TheA engagement of contacts LH205, along with the delayed engagement of contacts P 221, placesdischarge resistances 32 and 33 in parallel with the brake release coil30 to soften the application of the brake.

With the sequence of operations as above described the car will beslowed down and stopped level with the desired landing without sacrificeof smoothness. However, should the car .switch be centered with the carata greater distance from the landing, the maintaining relay would holdin to effect, through its contacts M 164, the retention of the maindirection switch and main brake and lield switch in operated condition.Should relay M drop out before the levelling switch'contacts engage, thesubsequent engagement of the levelling switch contacts as the levellingswitch roller rides on to the cam would cause the operation of switchesLB and LH and relay LF to bring the car to a level with the floor. Inthe event that the car switch is centered late in the stoppingoperation, as for example when the levelling switch operating rollerstrikes the levelling ram upon the dropping out of the irst acceleratingswitch D, the immediate separation of contacts LH 212 forces' thedropping out of the main direction switch and the main brake and fieldswitch to. permit the immediate change of the field winding connectionsand thus slow down the elevator motor more rapidly. In this manner thetendency for the car to overrun the Hoor is reduced.

Should an overrun occur, however,' the system is arranged so that theoperation of the vswitches is modiied. Assuming in the above examplethat the car overruns the third floor landing to the extent of causingthe engagement of levelling switch down slow speed contacts 35, acircuit is completed for down levelling direction switch actuating coilLC 228 and coil LH 190. This circuit may be traced from the left-handblade of switch 47, by way of line 55 through contacts A 60, line 191,contacts 35, by way of line 230 through coil LC 228, by way of line 192through coil LH 190, line 85, to the rightcause the separat-ion ofcontacts L 118 and L 121 and the engagement of contacts L 216, L 217, L218 and L 220. 'The switch LC operates to 'cause the separation ofcontacts LC 133 and the engagement of contacts LC l231, LC 232 and LC233. :The separation of contacts LC 133 is without particular effect atthis time. The separation of contacts LH 206, L 118 and L 121 and theengagement of conta-cts LC 231, LC 232, L 216 and L 217 causes thedisconnection of the separately excited ield winding from the generatorarmature and the connection of portions 17 and 18 of the winding to themains in such manner as tocause their magnetizing forcesto act inopposition. The engagement of contacts LH 211 and L 220 short-circuitsrsistance sections 155 and 165, causing the application of the desiredvoltage to the generator separately excited field winding. Resistance28, reconnected across portion 18 of the winding, as before causes lesscurrent iiow through portion 18 than through portion 17. Due to thereversal of the flow of current throu h both portions of the separatelyexcited fie d winding from that during the levelling operation upon thecar approaching the floor in the up direction, thecar is caused to startin the down direction.

VThe engagement of contacts LC 233 completed a circuit for the downseries eld relay actuating coil G 234 and the down hard brake switchactuatin coil P 227. This circuit may betraced rom the left-hand bladeof switch 47 by way of line 55 through contacts 60, by way of line 235.through contacts LC 233, coil G 234, coil P 227 and portion 236 ofreactancel X 203, line 204, by way of line 58 throu h contacts A 61, tothe righthand blade ofg switch 47. Relay G and witch P do not operateimmediately upon he engagement of contacts LC 233. When approaching thefloor in the up direction, the current flowin through reactance portion202 caused a ux to be built u in the reactance X 203 in one direction.pon the separation of contacts LB 197, the current in the reactance andcoil P 200 discharged into resistance 226 tending to maintain the fluxbuild up and, as previously ex lained, switch P in o erated condition.pon the engagement o contacts 'LC 233 on the overrun, thecurrentsupplied to coils G 234 and P 227 must reverse the flux in thereactance, thus taking a longer time to build up to a value sufiiclentto cause the operation of relay G and switch P. Thus contacts F 225,depending for their operation upon the operation of relay G, remainclosed temporarily to insure that the current in the generatorarmature-motor armature circuit has fallen to a low value. Since thecurrent in the rection such as to cause the generation of an E. M. F.which is of proper polarity for operating the car in the down direction,immediate increase in the strength of the series field might result inan overrun in the down direction. As the car returns to the floor, it isstopped by the separation of the levelling switch slow speed contacts 35in a manner similar to that described for approaching the floor in theup direction.

lf the overrun is great enough to 'cause the engagement of the levellingswitch down fast speed contacts 37. as well as the levelling switch downslow speed contacts 35, coil LF 193 is energized. As before, relay LFcauses the engagement of contacts LF 213 to shortcircuit resistancesection 166, increasing the generator voltage and causing the elevatormotor to run at its fast levelling speed. Re.

lay LF also causes the engagement of contacts LF 214 toenergize coil J82 again in the event that it has become deenergized. U on such anoverrun, the automatic gate and oor opening operation does not occuruntil contacts LF 214 separate, as previousl described. Further thanthis, the operatlon on an overrun is as above described.

It is to be understood that the operator may control both theacceleration and retardation of the car by moving the car switch insteps. In the event that the operator starts the car from a fioor bymoving the car switch only so far as to engage' one of the feedcontacts, for example contact 64, the up main direction switch B andmain brake -and field switch are operated to com lete the circuit forthe generator fieldpwin ing,

by the engagement of contacts B 111 and contacts B 112, and to cause therelease of the brake, by the engagement of contacts H 124. As theactuating coil of the first accelerating switch D is not energized, thisswitch does not operate and the levelling switch motor is not energizedto move the levelling switch rollers to clear the cams. The levellingcontrol relay R, however, operating along with switches B and H, causesthe separation of contacts R 241 and thus prevents the energization ofthe down levellin switch actuatin .coil LC 228 as a result o theoperation of t e levelling switch during the upward movement of the caraway from the fioor. Contacts LC 231 and LC 232, therefore, do notengage, preventing the establishing of a shunt circuitaround thegenerator separately excited field winding. Should the operator suddenlymove the car switch from one position into the other, for example fromup into down position, injury to the system is prevented by contacts B110 which remain separated until the up direction switch drops out. Itis to be noted that, when the car is suddenly reversed or stoppedbetween floors or stopped by opening the safety switch 50, the switch Pis not operated. Thus contacts P 221 are in engagement and a softapplication of' the brake is obtained.

In variable voltage control systems of the type wherein the elevatormotor is supplied with current from the generator of a motorgeneratorset, the generator is required to operate over a wide range of E. M. F.values, varying from a maximum in one direction to a maximum in theother. When operating at low values, the E. M. F. generated, with agiven field current, may vary over a wide range due to the varyingeffects of residual flux. This effect is very marked under levellingoperating conditions where low values of generated E. M. F. areemployed. Such low values of E. M. F. are usually obtained by permittingonly a small amount of current to ow through the generator separatelyex` cited field winding so as to produce low values of flux. Thus theresidual flux present forms a large ercentage of the total flux andtherefore a ects the operation of the system very markedly. In orderthat the effects of the residual flux ma erence may be had to tlieassumed hysteresis curve shown in Figure 3. This figure illustrates theconditions when a small current is supplied to" the separately excitedfield winding of a generator, as during the leveling operation. Themagnetizing forces due to this small current are represented as NI and-NI, depending on whether the car is approaching the fioor, or returningto the fioor after an overrun. Assume that the generator armature E. M.F. has been of the value V1 and that later, in attempting to make alanding, the self-levelling operation takes be clearly seen, refplacewith the car approaching the floor. The E. M.- F. of the generatorduring this period will be of a value V2. On'the other hand, if the caroverruns the floor, the E. M. F. of the generator will be of a value V2,which value is much less than the value V2. Hence the speed of theelevator motor is much less. The values V2 and V3 of the .generator E.M. F. may vary during operation of the system depending u n the previousmagnetic st-ate of the mac ine. Assuming that the E. M. F. values V2 andVs are those obtained during levelling for normal operation, then thevalues of -generator E. M. F. during levelling will lie somewherebetween V2 and V2 for other Iconditions of operation. Obviously, suchlarge. voltage variations would result in undesirable variations inoperation under levelling conditions. These variations cannot besatisfactorily corrected merely by adjusting the amount of resistance inseries with the separately excited field winding. For example, if theamount of resistance were decreased in order to raise the value of V3,the value V2 also would be increased, resulting in an increasingtendency to run past the floor. Similarly,if the amount ofresistance'were increased in order to lower the value-of V2, the valueof Va also would be lowered, which value might be too low to effect thereturn of the car to the lioor after an overrun. If the effects oflresidual flux are eliminated for levelling operating conditions, thesystem may be adjusted so as to obtain more uniform operation. This maybe accomplished by reversing the polarit of certain of the field poles.The preferre arrangement'for eecting this change has already beendescribed in connection with Figure 1. The particular arrangement of theseparately excited field winding is illustrated in Figure 2.

Referring to Figure 2, it is preferred to group the coils for the northand south poles N and S together to form the portion 17 and those forthe north and south poles N1 and S1 together to form the portion 18. Thecoils forming the portion 17 are connected in series relation as arethose forming the portion 18. With thel switch L in deenergizedposition, as during car switch operation, the current flows through thecoils in such'manner as to provide the poles of alternate polarity asindicated. Upon the operation of switch L during the levellingoperation, contacts L 118 and L 121 separate and contacts L` 216 and L217 engage. Although this operation does not affect the direct-ion ofthe flow of current through the coils for poles N and S, it does reversethe current through thecoils for poles N1 and S1. Thus N1 becomes asouth pole and S1 becomes a north pole. If these poles were excitedequally, thel value of the total E. M. F. at the generator brushes 19would bey substantially zero, since the voltage generated in part of thegenerator armature is balanced out by a voltage of equal value butopposite polarity generated in the remainder of the armature. "e Byemploying a large magneting force for each pole, with the magnetizingforce for the poles N1 and S1 excited by field winding portion 18 ofless value than that for poles N and S excited by portion 17, an E. M.F. of low value suitable for the levelling operation may be obtained. Inthis manner, the iron of the various parts of the magnetic circuit isworked on high portions of the hysteresis loop where the effect ofresidual flux is practically nil, and E. M. F.s may be obtained, duringlevelling operations, the values of which are `not affected by residualflux andare practically the same whether the car overruns or underrunsthe fioor. This may be accomplished by short-circuiting resistance 27with contacts L 220, LH 211 and LF 213 and by connecting resistance 28in parallel with portion 18, employing contacts L 218. The abovedescribed arrangement will operate to obviate the eHects of hysteresiswith generators of other pole numbers, a four pole generator beingchosen merely for convenience of description. In describin theinvention, the usual series armature wlnding has been assumed. If foranyreason, such as due to the manner of winding the generator armature, anE. M. F. is generated upon reversal ofportion 18 of the field windingwithout reducing the current therethrough,it would be of advantage sincea resistance of higher ohmic value could be employed for resistance 28.If the E. M. F. were great enough, re-

. sistance 28 could be dispensed with entirely.

1t is to-be understood that other arrangements may be emplo ed forcausing the ma netzing force for t e poles excited by fie d windingportion 18 to be different from the magnetizing force .for the polesexcited by winding portion 17 for example, as' by winding the coilsconstituting winding portion 18 so as to have a different number ofturns from the number-of turns of the coils constitutingv windingportion 17. If such arrangement were employed, resistance 28 might beomitted.

This arrangement for the control of the separately excited field windingalso is efi'ective in avoiding the occurrence of excessive speeds of theelevator car during the levellingperiod. The automatic opening of thegate and doorI during this period renders this feature of particularimportance. In systems employing resistance in series with the elevatormotor armature to control the speed of the motor during levelling, orwhere the voltage applied to the armature of the elevator motor duringlevelling is controlled by mea'ns of resistance in series with theseparately excited field winding of the generator which supplies powerto the motor, there is n is short-circuited duringlevelling in order toobtain the desired fast levelling speed. Thus it is impossible to obtainexcessive speeds of the elevator car during the gate and door openingoperation by the application of line voltage tothe generator separatelyexcited ield as the most that could happen would beto cause the car torunat its fast levelling speed. It is to be understood that contactscould be provided on the field control switch L to break the circuitforthe gate motor maintaining relay coil K 130 instead of employingcontacts LB 132 and LC 133 in order to insure that the gate and doorWould not open unless the field Winding connections were changed. j i

As many changes could be made in the above arrangement and manyapparently Widely different embodiments of this invention could be madeWithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. VIn combination; a generator having an armature, a plurality of polepieces and a field winding arranged for separate excitation, saidWinding` comprising a plurality of field coils, one on each pole piece;means for drivling said generator armature; a source of current ofsubstantially constant voltage value for said field Winding; means forcausingthe generation of full Voltage at the generator terminals withsubstantially the full value of said source voltage applied to saidWinding and with said' armature driven at a certain speed, said secondnamed means comprising means for connecting said coils to said source insuch manner that adjacent pole pieces are excited for oppositepolarities; and means for causing the generation of a low voltage at thegenerator terminals with s'ubstantialli7 the full value of lsaid sourcevoltage applied to saidv Winding and with said armature driven at saidcertain speed, said last included means comprising means for connectingsaid coils to said source in -sucli manner that each of said pole pieceshas at least one adjacent pole piece of like polarity.

2. In combination; a generator having an armature, a plurality of polepieces, a plural- =drivenat a certain speed, said second named meanscomprising means for connecting said coils to said source in suclimannerthat adj acent pole pieces are excited for opposite polarities; aresistance; and means for causing the generation of a low voltage atsaid 'brushes with substantially the full value of said source voltageappliedto said Winding and with said armature driven at said certainspeed, said last included means comprising .means for reconnecting saidcoils to said source invsuch manner that each of said pole pieces has atleast one adjacent pole pieceof like polarity and for connecting saidresistance in parallel with a portion of said winding.

3. In combination; a generator having an armature, a plurality of polepieces, a plurality of brushes of a number equal to the number of polepieces and a field Winding arranged for separate excitation, saidwinding comprising a plurality of field coils, one on each pole piece;means for driving said generature armature; a. source of current ofsilbstaiitially constant voltage Value for said field Winding; means forcausing the generation of full voltage at said brushes withsubstantially tlie full Value of said source voltage applied to saidwinding and with said armature driven at a certain speed, said secondnamed means comprising means for connecting said coils to said source insuoli manner that adjacent pole pieces are excited for oppositepolarities; a resistance; means for causing the generation of a lowvoltage of a certain -value at said brushes with substantially the fullvalue of said source voltage applied to said Winding and with saidarmature driven at said certain speed, said third named means comprisingmeans for reconnecting said coils to said source in such manner thateach of said pole pieces has at least one adjacent pole piece of likepolarity and vfor connecting said resistance in parallel with a portionof said Winding; and means for causing current to flow ineitherdirectionthrough all of said coils as reconnected to cause said low voltage atsaid brushes to be of either polarity.

4. In combination, a motor, a variable voltage generator for supplyingcurrent'to said motor, said generator having a field Winding, a sourceof current for said winding, means for causing the motor to run at acertain speed, said means comprising means for connecting said fieldwinding to said source,A means for causing the motor to run at a slowerl speed, said lastI included means comprising name to thisspecification.

, .ANTHONY PINTO.

